The vitamin E is the most important natural antioxidant. The pathway for synthesis of the tocopherol in plant is described in detail later, for example, the pathway is mentioned in the literature of Collakova et al. (Collakova et al., Plant Physial., 133 (2003) p930-940) or the general remarks of Bowier et al. (Bowier et al., Progress in Lipid Res., 44 (2005) p414-416). In addition, as to the vitamin E of Para rubber tree, it is described that tocotrienol was isolated from Para rubber tree (Hevea brasiliensis) and identified in the literature of Whittle et al. (Whittle et al., Biochem. J., 100 (1966) p138-145) or the literature of Dunphy et al. (Dunphy et al., Nature, 207 (1965) p521-522).
As for the gene of enzyme derived from plant related to biosynthesis of the vitamin E, till now, the following examples are reported: the geranylgeranyl reductase derived from thale cress (Arabidopsis thaliana) was isolated (Keller et al., Eur. J. Biochem, 251 (1998) p413-417); the mutation of tocopherol cyclase gene caused to accumulate the precursor of 2,3-dimethyl-5-phytyl-1,4-benzoquinone into the leaves or seeds (Sattler et al., Plant Physiology, 132 (2003) p2184-2195 and Schledz et al., FEBS letter, 499 (2001) p15-20); the homogentisic acid geranylgeranyl transferase gene derived from barley was introduced into Arabidopsis or corn to be successful in control of the vitamin E content, composition (Cahoon et al., Nature Biotechnology, 21 (2003) p1082-1087), the γ-tocopherol methyl transferase gene derived from thale cress was introduced into thale cress to be successful in control of the vitamin E composition (Shintani et al., Science, 282 (1998) p2098-2100); the γ-tocopherol methyl transferase gene and the 2-methyl-6-phytyl benzoquinone methyl transferase gene derived from thale cress were introduced into soy bean to be successful in control of the vitamin E content, composition (Eenennaam et al., The Plant Cell, (2003) p3007-3019). In addition, as to the transgenic soy bean that the α-tocopherol content was raised, the patent application has been filed (Japanese Patent Application Laid-Open No. 2006-075106A bulletin). However, in the Para rubber tree, the gene of enzyme related to biosynthesis of the vitamin E was not acquired at all till now. Therefore, there was no means to control biosynthesis of the vitamin E in Para rubber tree till now.
Furthermore, FIG. 1 shows the biosynthetic pathway of the vitamin E of plant that has ever understood. Using prephenic acid as substrate, p-hydroxyphenyl pyruvic acid is generated by the action of prephenate dehydratase. And, by the action of p-hydroxyphenyl pyruvic acid dioxygenase, homogentisic acid is generated from p-hydroxyphenyl pyruvic acid. In addition, the nonmevalonate pathway acts on this synthesis, too, and phytyl diphosphate is generated from geranylgeranyl diphosphate by geranylgeranyl reductase.
From these products, benzoquinone derivative or plastoquinone derivative which is a precursor of the vitamin E is generated. In other words, from geranylgeranyl diphosphate and homogentisic acid, 2-methyl-6-geranylgeranyl benzoquinone is generated by the action of homogentisic acid geranylgeranyl transferase. In addition, from phytyl diphosphate and homogentisic acid, 2-methyl-6-phytyl benzoquinone is generated by the action of homogentisic acid phytyl transferase. Furthermore, from 2-methyl-6-geranylgeranyl benzoquinone and S-adenosyl-L-methionine, 2,3-dimethyl-5-geranylgeranyl-1,4-benzoquinone is generated by the action of 2-methyl-6-geranylgeranyl benzoquinone methyl transferase. In addition, from 2-methyl-6-phytyl benzoquinone and S-adenosyl-L-methionine, 2,3-dimethyl-5-phytyl-1,4-benzoquinone is generated by the action of 2-methyl-6-phytyl benzoquinone methyl transferase.
Tocotrienol is generated using them as raw materials. In other words, from 2,3-dimethyl-5-geranylgeranyl-1,4-benzoquinone, γ-tocotrienol is generated by the action of tocopherol cyclase, and from γ-tocotrienol and S-adenosyl-L-methionine, α-tocotrienol is generated by the action of γ-tocopherol methyl transferase. In addition, from 2-methyl-6-geranylgeranyl benzoquinone, δ-tocotrienol is generated by the action of tocopherol cyclase, and from δ-tocotrienol and S-adenosyl-L-methionine, β-tocotrienol is generated by the action of γ-tocopherol methyl transferase.
Furthermore, tocopherols are generated. In other words, from 2,3-dimethyl-5-phytyl-1,4-benzoquinone, γ-tocopherol is generated by the action of tocopherol cyclase, and from δ-tocopherol and S-adenosyl-L-methionine, α-tocopherol is generated by the action of γ-tocopherol methyl transferase. In addition, from 2-methyl-6-phytyl benzoquinone, δ-tocopherol is generated by the action of tocopherol cyclase, and from δ-tocopherol and S-adenosyl-L-methionine, β-tocopherol is generated by the action of γ-tocopherol methyl transferase.